Class Bidi

A Bidi object provides information on the bidirectional reordering of the text
used to create it. This is required, for example, to properly display Arabic
or Hebrew text. These languages are inherently mixed directional, as they order
numbers from left-to-right while ordering most other text from right-to-left.

Once created, a Bidi object can be queried to see if the text it represents is
all left-to-right or all right-to-left. Such objects are very lightweight and
this text is relatively easy to process.

If there are multiple runs of text, information about the runs can be accessed
by indexing to get the start, limit, and level of a run. The level represents
both the direction and the 'nesting level' of a directional run. Odd levels
are right-to-left, while even levels are left-to-right. So for example level
0 represents left-to-right text, while level 1 represents right-to-left text, and
level 2 represents left-to-right text embedded in a right-to-left run.

DIRECTION_RIGHT_TO_LEFT

DIRECTION_DEFAULT_LEFT_TO_RIGHT

public static final int DIRECTION_DEFAULT_LEFT_TO_RIGHT

Constant indicating that the base direction depends on the first strong
directional character in the text according to the Unicode
Bidirectional Algorithm. If no strong directional character is present,
the base direction is left-to-right.

DIRECTION_DEFAULT_RIGHT_TO_LEFT

public static final int DIRECTION_DEFAULT_RIGHT_TO_LEFT

Constant indicating that the base direction depends on the first strong
directional character in the text according to the Unicode
Bidirectional Algorithm. If no strong directional character is present,
the base direction is right-to-left.

Constructor Detail

Bidi

flags - a collection of flags that control the algorithm. The
algorithm understands the flags DIRECTION_LEFT_TO_RIGHT, DIRECTION_RIGHT_TO_LEFT,
DIRECTION_DEFAULT_LEFT_TO_RIGHT, and DIRECTION_DEFAULT_RIGHT_TO_LEFT.
Other values are reserved.

Bidi

The RUN_DIRECTION attribute in the text, if present, determines the base
direction (left-to-right or right-to-left). If not present, the base
direction is computes using the Unicode Bidirectional Algorithm, defaulting to left-to-right
if there are no strong directional characters in the text. This attribute, if
present, must be applied to all the text in the paragraph.

The BIDI_EMBEDDING attribute in the text, if present, represents embedding level
information. Negative values from -1 to -62 indicate overrides at the absolute value
of the level. Positive values from 1 to 62 indicate embeddings. Where values are
zero or not defined, the base embedding level as determined by the base direction
is assumed.

The NUMERIC_SHAPING attribute in the text, if present, converts European digits to
other decimal digits before running the bidi algorithm. This attribute, if present,
must be applied to all the text in the paragraph.

Parameters:

paragraph - a paragraph of text with optional character and paragraph attribute information

Bidi

Create Bidi from the given text, embedding, and direction information.
The embeddings array may be null. If present, the values represent embedding level
information. Negative values from -1 to -61 indicate overrides at the absolute value
of the level. Positive values from 1 to 61 indicate embeddings. Where values are
zero, the base embedding level as determined by the base direction is assumed.

Parameters:

text - an array containing the paragraph of text to process.

textStart - the index into the text array of the start of the paragraph.

embeddings - an array containing embedding values for each character in the paragraph.
This can be null, in which case it is assumed that there is no external embedding information.

embStart - the index into the embedding array of the start of the paragraph.

paragraphLength - the length of the paragraph in the text and embeddings arrays.

flags - a collection of flags that control the algorithm. The
algorithm understands the flags DIRECTION_LEFT_TO_RIGHT, DIRECTION_RIGHT_TO_LEFT,
DIRECTION_DEFAULT_LEFT_TO_RIGHT, and DIRECTION_DEFAULT_RIGHT_TO_LEFT.
Other values are reserved.

Method Detail

createLineBidi

Create a Bidi object representing the bidi information on a line of text within
the paragraph represented by the current Bidi. This call is not required if the
entire paragraph fits on one line.

Parameters:

lineStart - the offset from the start of the paragraph to the start of the line.

lineLimit - the offset from the start of the paragraph to the limit of the line.

isMixed

public boolean isMixed()

Return true if the line is not left-to-right or right-to-left. This means it either has mixed runs of left-to-right
and right-to-left text, or the base direction differs from the direction of the only run of text.

Returns:

true if the line is not left-to-right or right-to-left.

isLeftToRight

public boolean isLeftToRight()

Return true if the line is all left-to-right text and the base direction is left-to-right.

Returns:

true if the line is all left-to-right text and the base direction is left-to-right

isRightToLeft

public boolean isRightToLeft()

Return true if the line is all right-to-left text, and the base direction is right-to-left.

Returns:

true if the line is all right-to-left text, and the base direction is right-to-left

getLength

public int getLength()

Return the length of text in the line.

Returns:

the length of text in the line

baseIsLeftToRight

public boolean baseIsLeftToRight()

Return true if the base direction is left-to-right.

Returns:

true if the base direction is left-to-right

getBaseLevel

public int getBaseLevel()

Return the base level (0 if left-to-right, 1 if right-to-left).

Returns:

the base level

getLevelAt

public int getLevelAt(int offset)

Return the resolved level of the character at offset. If offset is <0 or >=
the length of the line, return the base direction level.

Parameters:

offset - the index of the character for which to return the level

Returns:

the resolved level of the character at offset

getRunCount

public int getRunCount()

Return the number of level runs.

Returns:

the number of level runs

getRunLevel

public int getRunLevel(int run)

Return the level of the nth logical run in this line.

Parameters:

run - the index of the run, between 0 and getRunCount()

Returns:

the level of the run

getRunStart

public int getRunStart(int run)

Return the index of the character at the start of the nth logical run in this line, as
an offset from the start of the line.

Parameters:

run - the index of the run, between 0 and getRunCount()

Returns:

the start of the run

getRunLimit

public int getRunLimit(int run)

Return the index of the character past the end of the nth logical run in this line, as
an offset from the start of the line. For example, this will return the length
of the line for the last run on the line.

Parameters:

run - the index of the run, between 0 and getRunCount()

Returns:

limit the limit of the run

requiresBidi

public static boolean requiresBidi(char[] text,
int start,
int limit)

Return true if the specified text requires bidi analysis. If this returns false,
the text will display left-to-right. Clients can then avoid constructing a Bidi object.
Text in the Arabic Presentation Forms area of Unicode is presumed to already be shaped
and ordered for display, and so will not cause this function to return true.

Parameters:

text - the text containing the characters to test

start - the start of the range of characters to test

limit - the limit of the range of characters to test

Returns:

true if the range of characters requires bidi analysis

reorderVisually

Reorder the objects in the array into visual order based on their levels.
This is a utility function to use when you have a collection of objects
representing runs of text in logical order, each run containing text
at a single level. The elements at index from
objectStart up to objectStart + count
in the objects array will be reordered into visual order assuming
each run of text has the level indicated by the corresponding element
in the levels array (at index - objectStart + levelStart).